Illustration
Autumn Sweetheart Encore Azalea
Rhododendron 'Robleja'
Also called autumn sweetheart and encore autumn sweetheart
Autumn Sweetheart Encore Azalea blooms from May through October.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Autumn Sweetheart Encore Azalea
Plant it in part shade. It prefers moderate water. It is hardy in USDA zones 6–9. Expect it to reach about 4 ft tall and 3.5 ft wide at maturity, in roughly 4 years (a house reading).
Is Autumn Sweetheart Encore Azalea toxic to dogs or cats?
- Listed as toxic to dogs and cats by NC State Extension, Pet Poison Helpline and Royal Horticultural Society.
- Listed as poisonous to people by NC State Extension and Royal Horticultural Society.
Lists differ and none is complete. If a pet eats a plant and seems unwell, call a veterinarian or a pet poison helpline.
What was checked
Mature height and spread, hardiness zones, sun, water, bloom months and color and the trait tags were checked against named botanical sources for this plant, with what the sources could not settle written down; years to mature size rests on a recorded house rule where no publisher states one, and is marked so; its common name and alternate names have not been checked yet. Each fact above carries its own mark. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Autumn Sweetheart Encore Azalea
Plant Autumn Sweetheart Encore Azalea in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 7, the middle of its hardy zones 6 to 9, spring means March to May and fall means September or October. Once settled, it blooms from May to October.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 7, the middle of this plant's hardy range, start with zone 7 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Autumn Sweetheart Encore Azalea get?
4 fttall5 ft 7 inan adult3.5 ftwideSee Autumn Sweetheart Encore Azalea in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Autumn Sweetheart Encore Azalea
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Autumn Sweetheart Encore Azalea about 3.5 ft apart, center to center, so each plant has room to reach its full width.
Add Autumn Sweetheart Encore Azalea to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Autumn Sweetheart Encore Azalea's height, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases, pests and toxicity were checked against 8 published sources on October 5, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- Missouri Botanical GardenPlant Finder, Rhododendron 'Robleja' AUTUMN SWEETHEARTheight, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases and pests
- NC State ExtensionGardener Plant Toolbox, Rhododendron Encore Groupheight, spread, hardiness zones, sun, water, bloom months and color, soil, diseases, pests and toxicity
- US plant patent (Google Patents)the breeder's own registration, full text via the Google Patents mirrorheight, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil and pests
- encoreazalea.comEncore Azalea (Plant Development Services, the breeder and introducer)height, spread, hardiness zones, sun, water, bloom months and color, trait tags and soil
- kiefernursery.comKiefer Landscaping & Nursery, Durham NCheight, spread, hardiness zones, sun, water, bloom months and color and pests
- Plant Addictsheight, spread, hardiness zones, sun, water, bloom months and color and soil
- plants.ellishomeandgarden.comNetPS Plant Finder record (Ellis Home & Garden plant library, Louisian...height, spread, hardiness zones, sun, water, bloom months and color and soil
- ASPCAAnimal Poison Controltoxicity
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Autumn Sweetheart Encore Azalea
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
All parts contain grayanotoxins. Toxic to dogs, cats and horses: vomiting, diarrhea, weakness, and in serious cases cardiac failure. Pets and livestock are poisoned more readily than people. per ASPCA
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Design a garden with this
Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.